Introduction to Data Structures 자료구조개론 2019 Spring Semester

1. Introduction to Data Structures 자료구조개론2019 Spring Semester JoonwonLee College of Software

2. Instructor information • Joonwon Lee • Professor in College of Software • Research areas • Computer Systems • Contact information • joonwon@skku.edu • http://csl.skku.edu/People/Joon • Corporate Collaboration Center #85572 • Office hour: by appointment

3. Course information • Class hours • Tuesday 12:00 – 13:15 • Thursday 13:30 – 14:45 • Language: English • Classroom: 23217 • Prerequisite: C programming language • You SHOULD know how to program using C (e.g., pointer) • If you don’t know how to use pointer, please drop this course! • Course website • http://www.icampus.ac.kr

4. What is this course? • In computer science, a data structure is a data organization, management and storage format that enables efficient access and modification.More precisely, a data structure is a collection of data values, the relationships among them, and the functions or operations that can be applied to the data. [Wikipedia] • Class goals • Learn data structure, which is a way of collecting and organizing data in a computer to perform operations on the data efficiently • Cover arrays, stacks, queues, linked lists, tree, graph, hashing, search and sorting algorithms

5. Lecture notes • Textbook • Fundamentals of data structures in C by Horowits, Sanhni and Anderson-Freed (2nd, 2008) • Lecture Notes • Adapt Prof. Jinkyu Lee’s slides • which is also from Prof. Jongwuk Lee’s slides.

6. Grading • Attendance: 10% • You will be given F if you are absent eight times or more. • Alternative attendance approval: to follow SKKU rule • Assignments: 30% • Four programming homeworks • Academic honesty is truly needed since the penalty is severe • Mid-term exam: 30% • Final exam: 30%

7. Grading • If you have any plan to be absent with reasonable reasons, please tell me in advance! • Cheatingwill lead you to fail this course with “F” grade. • You will be given F if you are absent eight times or more. • The 50% A and 90% guideline is merely an upper-limit by SKKU.

8. Tentative schedule and topics

9. Tentative schedule and topics

10. TA • To be updated

11. Do we have to use only English? • You are recommended to use English only. • Assignment • Your program (C code): only in English • Your report: either in English or Korean • Exam • All questions: written in English • Your answers: either in English or Korean • Outside of the class • Questions through email: either in English or Korean • In-class • ?

12. Any question? • And, any suggestion?

13. Basics of data structures

14. Definition • Definition of data structure • An organization of information, usually in memory, for better algorithm efficiency • Queue, stack, linked list, heap, dictionary, tree, etc. • Definition of algorithm • What is an algorithm? • What is an efficient algorithm? • An algorithm which spends less resources: time and space

15. Definition • Definition of an algorithm: a finite set of instructions that should satisfy 1) Input: zero or more inputs 2) Output: at least one output 3) Definiteness: clear and unambiguous instructions 4) Finiteness: terminating after a finite number of steps 5) Effectiveness (Machine-executable): basic enough to be carried out

16. Program • Program Program = Data Structure + Algorithm How to store data in computer memory How to handle the stored data

17. Example • Example 1 • Question 1: sort 100 records. • Question 2: sort 1,000,000 records.

18. Example • Example 2 • Question 1: You have a lot sorted data. You frequently search for some data. • Question 2: You have the same data. You frequently insert and delete some data.

19. Overview • What to learn in Data Structure • Some theory and data structure to efficiently store and manipulate data • Some algorithms and examples • Example • Data structure: array, list, queue, tree, graph, sorting, hashing, heap, etc. • Algorithm: sorting, searching, minimum spanning tree, shortest path algorithm, etc. • Theory: abstract data types, performance analysis

20. Algorithm Course Data Structure Course Data Structure + Algorithm Data Structure+ Algorithm Overview • Data Structure course vs. Algorithm course Program = Data Structure + Algorithm

21. Review on C Programming

22. Review on C Programming • What should you do with the C programming? • How to use an array and a pointer • Understand the relationship between the array and the pointer. • Use dynamic memory allocation. • How to define a structure and make use of it • Understand self-referential structures. • How to use recursiveprogramming • Transform iterative programming into recursive programming. • To take this course, Istronglyrecommendthat youhavetakenCprogramming!

23. WhatisArray? • Definition • A collection of elements with same data types • Each element is sequential in memory. • Array index • Each element can be referenced by an index. • Index ranges: [0] ~ [size – 1] intscore[10]; Data type Array name Array size

24. Example: Array • Input five numbers and print them reversely. #include<stdio.h> #defineARRAY_SIZE 5 int main() { int numbers[ARRAY_SIZE], i; printf("Input five numbers\n"); for (i = 0; i < ARRAY_SIZE; i++) scanf("%d", &numbers[i]); for (i = ARRAY_SIZE - 1; i >= 0; i--) printf("%d ", numbers[i]); return 0; }

25. Function Call with Array • Calculating the average of values in array #include<stdio.h> #defineARRAY_SIZE 5 voidinputNumbers(intnum[], intlen); doublecomputeAverage(intnum[], intlen); int main() { int numbers[ARRAY_SIZE]; inputNumbers(numbers, ARRAY_SIZE); printf("average: %.3lf", computeAverage(numbers, ARRAY_SIZE)); return 0; }

26. Function Call with Array • Calculating the average of values in array voidinputNumbers(intnum[], intlen) { inti; for (i = 0; i < len; i++) scanf("%d", &num[i]); } doublecomputeAverage(intnum[], intlen) { int total = 0, i; for (i = 0; i < len; i++) total = total + num[i]; return total / (double)len; }

27. Two-Dimensional Array • Filling all entries in the two-dimensional matrix int row, col, matrix[6][6]; for (row = 0; row < 6; row++) { for (col = 0; col < 6; col++) { if (row < col) matrix[row][col] = 1; elseif (row == col) matrix[row][col] = 0; else matrix[row][col] = -1; } }

28. int scores[10]; int matrix[6][6];

29. What is Pointer? • Definition • A variable to store a memory address instead of a value intn = 3; 0070FA44 Address 00FDFC18 n pn Name Value 3 00FDFC18 int* pn = &n; Variable

30. & (Ampersand) Operator • Reference operator • Return the address of an variable. char* pc 00FDFC18 #include<stdio.h> int main() { char c = 'A'; char *pc = &c; printf("%c %p\n", c, pc); printf("%p %p\n", &c, &pc); printf("%d %d\n", sizeof(c), sizeof(pc)); return 0; } 00FDFC1C 00FDFC19 pc 00FDFC1A 00FDFC1B c 00FDFC1C 65 (‘A’) 00FDFC1D 00FDFC1E 00FDFC1F pc c 65 (‘A’)

31. & (Ampersand) Operator • What is the size of a pointer variable? int* pn 00FDFC18 #include<stdio.h> int main() { int n = 3; int*pn= &n; printf("%d %p\n", n, pn); printf("%p %p\n", &n, &pn); printf("%d %d\n", sizeof(n), sizeof(pn)); return 0; } 00FDFC1C 00FDFC19 pn 00FDFC1A 00FDFC1B 00FDFC1C 3 00FDFC1D n 00FDFC1E 00FDFC1F pn n 3

32. * (Asterisk) Operator • Dereference operator • Return the value at the pointer address. #include<stdio.h> int main() { char c = 'A'; char *pc = &c; printf("%c %c\n", c, *pc); *pc = 'C'; printf("%c %c\n", c, *pc); return 0; } char *pc 00FDFC18 00FDFC1C 00FDFC19 pc 00FDFC1A 00FDFC1B c 00FDFC1C 67 (‘C’) 00FDFC1D 00FDFC1E 00FDFC1F

33. Example: Pointer • Use address and dereference operators correctly. #include<stdio.h> int main() { int a, b, c; int*p, *q, *r; a = 6, b = 10; p = &b, q = p, r = &c; p = &a, *q = 8, *r = *p; *r = a + *q + *&c; printf("%d %d %d", a, b, c); return 0; }

34. Example: Pointer #include<stdio.h> int main() { int a, b, c; int*pa = &a, *pb = &b, *pc = &c; *pa = 10, *pb = 20; *pc = *pa + *pb; printf("%d %d %d", a, b, c); return 0; }

35. Functional Call with Pointer • Two types for inter-function communication • Call by value: passing by value • Call by reference: passing by address #include<stdio.h> void swap1(int x, inty); void swap2(int* px, int* py); int main() { int a = 5, b = 7; swap1(a, b); printf("%d %d\n", a, b); swap2(a, b); printf("%d %d\n", a, b); return 0; } void swap1(int x, inty) { int temp = x; x = y; y = temp; } void swap2(int* px, int* py) { int temp = *px; *px = *py; *py = temp; }

36. Pointer to Pointer • Wecan use a pointer that points to another pointer. char **ppc #include<stdio.h> int main() { char c = 'A'; char* pc = &c; char** ppc = &pc; printf("%p %p\n", pc, ppc); printf("%d %d\n", sizeof(pc), sizeof(ppc)); return 0; } &ppc 0062FD78 00FDFD84 0062FD79 ppc 0062FD7A 0062FD7B 00FDFD84 &pc 0062Fd90 00FDFD85 pc 00FDFD86 00FDFD87 c 0062Fd90 65 (‘A’) &c 0062Fd91

37. Arithmetic Operation for Pointer • How does the char pointer work? #include<stdio.h> int main() { char c = 'A'; char* pc = &c; char** ppc = &pc; printf("%p %p\n", pc, ppc); printf("%p %p\n", pc + 1, ppc + 1); printf("%p %p\n", &c, &c + 1); printf("%p %p\n", &pc, &ppc); printf("%p %p\n", &pc + 1, &ppc + 1); return 0; } char **ppc &ppc 0062FD78 00FDFD84 0062FD79 0062FD7A 0062FD7B 00FDFD84 &pc 0062Fd90 00FDFD85 00FDFD86 00FDFD87 c 0062Fd90 65 (‘A’) &c 0062Fd91

38. Arithmetic Operation for Pointer • How does the int pointer work? int** ppn #include<stdio.h> int main() { int n = 10; int* pn = &n; int** ppn = &pn; printf("%p %p\n", pn, ppn); printf("%p %p\n", pn + 1, ppn + 1); printf("%p %p\n", &n, &n + 1); printf("%p %p\n", &pn, &ppn); printf("%p %p\n", &pn + 1, &ppn + 1); return 0; } &ppn 0062FD78 00FDFD84 +1 0062FD79 ppn 0062FD7A 0062FD7B &pn 00FDFD84 0062Fd90 00FDFD85 pn 00FDFD86 00FDFD87 &n 0062Fd90 20 0062Fd91 n 0062Fd92 0062Fd93

39. Array and Pointer • The pointer to the first element of the array can be used as the name of the array. #include<stdio.h> int main() { int a[6] = { 5, 3, 1, 2, 4, 6 }; int* pa = a; printf("%d %d\n", *a, *pa); printf("%p %p\n", a, pa); printf("%p %p\n", &a, &pa); printf("%d %d\n", a[0], pa[0]); printf("%d %d\n", a[1], pa[1]); return 0; } inta[6]; 4Byte a 00FDFC18 a[0] *(a + 0) 5 00FDFC1C a[1] 3 *(a + 1) 00FDFC20 1 a[2] *(a + 2) 2 00FDFC24 a[3] *(a + 3) 4 00FDFC28 a[4] *(a + 4) 6 00FDFC2C a[5] *(a + 5) 00FDFC30 pa 00FDFC18 00FDFC3C

40. Example: Array and Pointer • Is it a correct code? #include<stdio.h> int main() { int a[6] = { 1, 2, 3, 4, 5, 6 }; int*pend = a + 6; int *pi = NULL; for (pi = a; pi < pend; pi++) printf("%d\n", *pi); return 0; } a pi 00FDFC18 1 00FDFC1C 2 00FDFC20 3 00FDFC24 4 5 00FDFC28 6 00FDFC2C pend -1440986684 00FDFC30

41. Example: Array and Pointer • Print the smallest array value using pointers. #include<stdio.h> int main() { int a[6] = { 32, 12, 31, 42, 15, 24 }; int*pend = a + 6; int*psmallest = a; int *pi = NULL; for (pi = a; pi < pend; pi++) { if (*pi < *psmallest) psmallest = pi; } printf("%d", *psmallest); return 0; } psmallest a 00FDFC18 32 00FDFC1C 12 00FDFC20 31 00FDFC24 42 15 00FDFC28 24 00FDFC2C pend -1440986684 00FDFC30

42. Passing Array to Function • Passing a pointer (instead of an array) to a function #include<stdio.h> voidprintArray(int* pa, intlen); int main() { int a[5] = { 5, 3, 2, 1, 4 }; printArray(a, 5); return 0; } voidprintArray(int* pa, intlen) { inti; for (i = 0; i < len; i++) printf("%d\n", pa[i]); } inta[5]; 4Byte a 00FDFC18 a[0] 5 00FDFC1C a[1] 3 00FDFC20 2 a[2] 1 00FDFC24 a[3] 4 00FDFC28 a[4] 00FDFC2C pa 00FDFC18 00FDFC30

43. Example: Passing Array to Function • Multiplying 4 for each element in an array #include<stdio.h> void multiply4(int* pa, intlen); int main() { int a[5] = { 5, 3, 2, 1, 4 }, i; multiply4(a, 5); for (i = 0; i < 5; i++) printf("%d\n", a[i]); return 0; } void multiply4(int* pa, intlen) { inti; for (i = 0; i < len; i++) pa[i] = pa[i] * 4; } inta[5]; 4Byte a 00FDFC18 a[0] 5 00FDFC1C a[1] 3 00FDFC20 2 a[2] 1 00FDFC24 a[3] 4 00FDFC28 a[4] 00FDFC2C pa 00FDFC18 00FDFC30

44. How to Use Memory in C • Conceptual view of memory used in C program

45. Dynamic Memory Allocation #include<stdio.h> #include<stdlib.h> int main() { int size, i; scanf("%d", &size); // Allocate dynamic memory int* pn = malloc(sizeof(int)* size); for (i = 0; i < size; i++) scanf("%d", &pn[i]); for (i = 0; i < size; i++) printf("%d\n", pn[i]); free(pn); // Release memory return 0; }

46. Dynamic Memory Allocation • Is it a correct code? #include<stdio.h> #include<stdlib.h> int*genNumbers(int size); int main() { int size, i; scanf("%d", &size); int*pn = genNumbers(size); for (i = 0; i < size; i++) printf("%d\n", pn[i]); return 0; } int*genNumbers(intsize) { inti; int*pn = malloc(4 * size); for (i = 0; i < size; i++) scanf("%d", &pn[i]); returnpn; }

47. Memory Leak • It occurs when a computer program incorrectly manages memory allocations. • Memory that is no longer used is not released yet.

48. Solving Memory Leak • Use a pair of allocation and deallocation together! #include<stdio.h> #include<stdlib.h> voidgenNumbers(int* pn, ints); int main() { int size, i; scanf("%d", &size); int* pn = malloc(4 * size); genNumbers(pn, size); for (i = 0; i < size; i++) printf("%d\n", pn[i]); free(pn); return 0; } voidgenNumbers(int* pn, ints) { inti; for (i = 0; i < s; i++) scanf("%d", &pn[i]); }

49. What is Structure? • Definition • A collection of multiple related elements • A single name including possibly several different types

50. What is Structure? • How to declare a structure • All elements in the structure should be related logically. #include<stdio.h> typedefstruct { char name[10]; int scores[3]; } STUDENT; int main() { STUDENT s1 = { "Alice", 80, 70, 60 }; printf("%s\n", s1.name); for (inti = 0; i < 3; i++) printf("%d\n", s1.scores[i]); return 0; }